The invention relates to a portable burner with a first injector nozzle for fuel gas, which is disposed adjacent a first primary air aspiration point at the entry end of a first mixer tube, with a spin producer which is disposed in the first mixer tube at a distance in front of the outlet end thereof forming a second nozzle with a nozzle axis, and with a second mixer tube whose internal cross section (F2) is greater than the internal cross section (F1) of the first mixer tube and is disposed concentrically with the outlet end of the first mixer tube directly producing a burner flame, has an entry end for the burner flame and second aspiration points for secondary air in the area of the outlet end of the first mixer tube, and extends in the direction of flow all the way to its outlet end.
The fuel gas is usually obtained by the evaporation of liquid gas such as propane, butane or mixtures thereof, and dispensing it under pressure control.
It is known that, when a gas stream enters into an initially quiet gaseous medium, it sets the latter in motion, entrains it to some extent and drives it in the same direction. This process, called the injector process, is based on friction, turbulence and diffusion processes. It takes place also in a free atmosphere. However, its effectiveness can be increased by causing these processes to take place under guidance in a tubular housing which is composed of nozzles, tube sections and inlet and outlet openings. Known examples are the ejector or jet pump, including the diffusion pump, and the gas burner, including the Bunsen burner that is so familiar in school instruction.
The initial impulse of the gas stream produced as a rule by a nozzle (conversion of pressure to velocity) is distributed to the entrained gas. If sufficient guidance is not provided the gas stream rapidly becomes increasingly larger in cross section and slower, until the energy is used up by friction and/or, after deduction of losses, has been reconverted to pressure.
Nevertheless, a gas stream into initially quiet air has a very appreciable reach, which can be seen in examples from daily living. A candle can be made to flicker, if not go out, by blowing with the breath even from a distance of two meters. At the take-off of a jet aircraft the backwash reaches kilometers into the landscape, so that successive take-offs have to be delayed until the atmosphere quiets down.
Media of different densities and/or temperatures are especially difficult to mix. A "temperature layering" takes place over long distances.
German Patent Disclosure Document 2,254,891 discloses gas burners of the kind described in the beginning, which are designed for shrinking or for welding plastic films and which consequently have to produce hot gas at low outlet temperatures In the published embodiments the second mixer tube is either A made in its entire length without openings, or B the openings extend all the way to the outlet end or, in any case, into the direct vicinity of the outlet end of the second mixer tube. The secondary air consequently flows substantially in an axial direction, which is to be further explained below.
In case A the second mixer tube is widened at the inlet end and forms with the adjacent walls of the combustion chamber an inlet cone or a kind of spatial pipe elbow which turns the aspirated cold air in the vicinity of the wall of the mixer tube into a purely axial direction before the cold air reaches the burner flame. Temperature equalization in this case can be accomplished only by the divergence of the flame jet and marginal turbulences. Since the outlet opening of the combustion chamber, however, is oval or slot-shaped, this can take place in only one plane. Temperature layering is thus maintained at least over a considerable length of the second mixer tube, so that at the outlet opening of the second mixer tube a temperature profile is produced with a maximum in the center: the hot core of the gas stream reaches correspondingly far.
In case B too, the second mixer tube is completely open at the inlet end. Due to the uniform distribution of the perforations over the entire length, or most of the length, of the mixer tube, this has virtually no effect. The hot gas stream acts as a free stream, and this is expressly mentioned As a result, the aspiration takes place substantially in the axial direction the cold air and the hot gas stream flow substantially parallel to one another, and a far-reaching gas stream with a hot core is formed, i.e., with a temperature layering that diminishes only gradually, i.e., with increasing distance from the combustion chamber, due to stream divergence and mixing.
It is common to all burners that, due to limited dimensions, unavoidable built-in hardware such as flame holders, divided aspiration ducts etc., different air/gas fuel ratios form in the flow and in the flame, and hence also locally defined zones of different temperatures which are clearly recognizable in the flame as bright and dark streaks or "schlieren."
When spin producers are used in the known systems for the production of a twisting flow, this intensifies the temperature layering, which cannot be eliminated even by the oval or slot-shaped end of the combustion chamber. This will be further discussed herein:
Through U.S. Pat. No. 4,013,395 it is known to separate a combustion chamber from the single mixer tube by a spin producer in the form of radial vanes serving as a flame holder By means of the spin producer, the initially still cold mixture of fuel gas and ambient air is set in rapid rotation which continues in the combustion chamber about its axis. Due to the centrifugal forces caused thereby, the relatively cooler (higher-density) gas streams are thrown against the wall of the combustion chamber and cool it, while the relatively hotter (lower-density) gas streams gather in a core zone. This core zone is the actual, very hot working flame, which extends far out of the burner orifice This known burner does not have a second mixer tube. Such a burner serves preferably for the welding and hard soldering of metals.
German Patent Disclosure Document 2,254,891 and U.S. Pat. No. 4,013,495 pursue diametrically opposite courses and aims.
European Patent Disclosure Document 0,240,751 discloses a low-pressure hand burner in which a hot flame core without a spin producer is separated from the combustion chamber wall by a surrounding stream of cool ambient air. Here, too, a hot, far-reaching flame is produced, which issues from the combustion chamber. The surrounding stream that cools the combustion chamber wall is produced by the aspiration of ambient air through the back end of the burner in which openings are present which produce an air stream parallel to the combustion chamber wall and directly adjacent thereto This parallel flow is wanted, and it makes any mixing difficult.
British Patent 304,938 discloses a burner of a different kind with two injection systems arranged in series for the aspiration of primary and secondary air, which is to be fixedly screwed to a fixed line with all nozzles aligned vertically. By means of several adjusting devices and the design specifications for the ducting, it is said to bring it about that the gas-air mixture completely fills the cross section of the passage following each nozzle, and achieves such a velocity of flow at graduated stoichiometric mixture ratios that the burner flame does not strike back into the passages. According to the provisions, no flame burns in the final, cold injection tube. Instead, a far-reaching, hot flame issues from the last orifice. Spinning of the gases within the burner is even to be expressly avoided.